Method of producing soot

ABSTRACT

A method of producing soot, including: combusting a first fuel stream and a first oxidizer at a burner face; combusting a second fuel stream and a second oxidizer at the burner face, wherein the second fuel stream and the second oxidizer are premixed in advance of the burner face and a second equivalence ratio of the second fuel stream and the second oxidizer is less than about 1; and combusting a silicon-containing fuel into a plurality of soot particles, wherein the second fuel stream and the second oxidizer are combusted between the first fuel stream and the silicon-containing fuel. Applying this method of producing soot to deposit a preform suitable for the manufacture of optical fibers.

This application is a divisional and claims the benefit of priority ofU.S. patent application Ser. No. 16/541,773, filed Aug. 15, 2019, whichclaims the benefit of priority to U.S. Provisional Application Ser. No.62/720,479 filed on Aug. 21, 2018, the content of which is relied uponand incorporated herein by reference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure generally relates to soot production,specifically to methods of producing silica soot and more specificallyto deposition of the soot on a substrate.

BACKGROUND

Outside vapor deposition is utilized in the formation of optical fiberpreforms. Outside vapor deposition involves the process of combustingone or more silicon-containing fuels to form silica soot. The silicasoot is then deposited on a bait rod or core cane to form the opticalfiber preform. In conventional outside vapor deposition systems, a jetof the silica soot may be produced under conditions which lead thesilica soot to be dispersed. The dispersed silica soot may lead to alower than ideal efficiency of soot capture. The dispersion of thesilica soot jet may be affected by a variety of properties related tothe combustion of the silicon-containing fuels. Dispersed soot notcaptured on the bait rod or core cane to form the optical fiber preformis generally either exhausted out of the deposition chamber and captureddownstream as a waste material or deposited undesirably on surfaces andcomponents within the deposition chamber, typically requiring time andeffort to remove and clean before initiating deposition of the nextoptical fiber preform. It is therefore generally desirable to minimizeboth the amount and relative fraction of soot not deposited or capturedon the optical fiber preform. Additionally, the process of combustingsilicon fuels in the outside vapor deposition process creates audiblenoise. In a large-scale soot generation operation, it may be desirableto reduce such noise. The magnitude of the audible noise may be affectedby a variety of properties related to the combustion of thesilicon-containing fuels.

SUMMARY OF THE DISCLOSURE

According to at least one feature of the present disclosure, a method ofproducing soot, includes: combusting a first fuel stream and a firstoxidizer at a burner face; combusting a second fuel stream and a secondoxidizer at the burner face, wherein the second fuel stream and thesecond oxidizer are premixed in advance of the burner face and a secondequivalence ratio of the second fuel stream and the second oxidizer isless than about 1; and combusting a silicon-containing fuel into aplurality of soot particles, wherein the second fuel stream and thesecond oxidizer are combusted between the first fuel stream and thesilicon-containing fuel.

According to another feature of the present disclosure, a method ofproducing soot, includes: combusting a first fuel stream and a firstoxidizer at a periphery of a burner face; combusting a second fuelstream and a second oxidizer at the burner face; and combusting asilicon-containing fuel into a plurality of silica soot particles at alift-off distance away from the burner face, wherein the lift-offdistance is from about 0.1 cm to about 0.8 cm from the burner face.

According to another feature of the present disclosure, a method ofproducing soot, includes: combusting a first fuel stream and a firstoxidizer at a burner face, wherein a first equivalence ratio of thefirst fuel stream and the first oxidizer is greater than about 1.6;combusting a second fuel stream and a second oxidizer at the burnerface, wherein a second equivalence ratio of the second fuel stream andthe second oxidizer is from about 0.1 to about 0.5; and combusting asilicon-containing fuel into a plurality of silica soot particles at alift-off distance away from the burner face, wherein the lift-offdistance is from about 0.1 cm to about 0.8 cm from the burner face.

The present disclosure extends to:

A method of producing soot, comprising:

combusting a first fuel stream and a first oxidizer at a burner face;

combusting a second fuel stream and a second oxidizer at the burnerface, wherein the second fuel stream and the second oxidizer arepremixed in advance of the burner face and a second equivalence ratio ofthe second fuel stream and the second oxidizer is less than about 1; and

combusting a silicon-containing fuel into a plurality of soot particles,wherein the second fuel stream and the second oxidizer are combustedbetween the first fuel stream and the silicon-containing fuel.

The present disclosure extends to:

A method of producing soot, comprising:

combusting a first fuel stream and a first oxidizer at of a burner face;

combusting a second fuel stream and a second oxidizer at the burnerface; and

combusting a silicon-containing fuel into a plurality of silica sootparticles at a lift-off distance away from the burner face, wherein thelift-off distance is from about 0.1 cm to about 0.8 cm from the burnerface and wherein the second fuel stream is combusted between the firstfuel stream and the silicon-containing fuel.

The present disclosure extends to:

A flame comprising the combustion product of an organosilicon compound,the flame having an ignition point situated at a lift-off distance froma face of a burner, the lift-off distance being in the range from 0.1cm-0.8 cm.

These and other features, advantages, and objects of the presentdisclosure will be further understood and appreciated by those skilledin the art by reference to the following specification, claims, andappended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The following is a description of the figures in the accompanyingdrawings. The figures are not necessarily to scale, and certain featuresand certain views of the figures may be shown exaggerated in scale or inschematic in the interest of clarity and conciseness.

In the drawings:

FIG. 1A is a cross-sectional view of a burner in operation;

FIG. 1B is a view of the face of the burner;

FIG. 2 is a flowchart of a method of producing soot, according to atleast one example;

FIG. 3A is a temperature model of a first comparative example;

FIG. 3B is an SiO₂ mass fraction model of the first comparative example;

FIG. 3C is an image taken of the first comparative example in operation;

FIG. 4A is a temperature model of a first example consistent with thepresent disclosure;

FIG. 4B is an SiO₂ mass fraction model of the first example;

FIG. 4C is an image taken of the first example in operation;

FIG. 5 is a side-by-side comparison of the SiO₂ mass fraction model ofthe first comparative example and the first example; and

FIG. 6 is a plot of audible noise as a function of frequency.

FIG. 7 is a plot of capture efficiency vs supplemental equivalenceratio.

DETAILED DESCRIPTION

Additional features and advantages of the disclosure will be set forthin the detailed description which follows and will be apparent to thoseskilled in the art from the description, or recognized by practicing thedisclosure as described in the following description, together with theclaims and appended drawings.

As used herein, the term “and/or,” when used in a list of two or moreitems, means that any one of the listed items can be employed by itself,or any combination of two or more of the listed items can be employed.For example, if a composition is described as containing components A,B, and/or C, the composition can contain A alone; B alone; C alone; Aand B in combination; A and C in combination; B and C in combination; orA, B, and C in combination.

In this document, relational terms, such as first and second, top andbottom, and the like, are used solely to distinguish one entity oraction from another entity or action, without necessarily requiring orimplying any actual such relationship or order between such entities oractions.

It will be understood by one having ordinary skill in the art thatconstruction of the described disclosure, and other components, is notlimited to any specific material. Other exemplary embodiments of thedisclosure disclosed herein may be formed from a wide variety ofmaterials, unless described otherwise herein.

For purposes of this disclosure, the term “coupled” (in all of itsforms: couple, coupling, coupled, etc.) generally means the joining oftwo components (electrical or mechanical) directly or indirectly to oneanother. Such joining may be stationary in nature or movable in nature.Such joining may be achieved with the two components (electrical ormechanical) and any additional intermediate members being integrallyformed as a single unitary body with one another or with the twocomponents. Such joining may be permanent in nature, or may be removableor releasable in nature, unless otherwise stated.

As used herein, the term “about” means that amounts, sizes,formulations, parameters, and other quantities and characteristics arenot and need not be exact, but may be approximate and/or larger orsmaller, as desired, reflecting tolerances, conversion factors, roundingoff, measurement error and the like, and other factors known to those ofskill in the art. When the term “about” is used in describing a value oran end-point of a range, the disclosure should be understood to includethe specific value or end-point referred to. Whether or not a numericalvalue or end-point of a range in the specification recites “about,” thenumerical value or end-point of a range is intended to include twoembodiments: one modified by “about,” and one not modified by “about.”It will be further understood that the end-points of each of the rangesare significant both in relation to the other end-point, andindependently of the other end-point.

The terms “substantial,” “substantially,” and variations thereof as usedherein are intended to note that a described feature is equal orapproximately equal to a value or description. For example, a“substantially planar” surface is intended to denote a surface that isplanar or approximately planar. Moreover, “substantially” is intended todenote that two values are equal or approximately equal. In someembodiments, “substantially” may denote values within about 10% of eachother.

It is also important to note that the construction and arrangement ofthe elements of the disclosure, as shown in the exemplary embodiments,is illustrative only. Although only a few embodiments of the presentinnovations have been described in detail in this disclosure, thoseskilled in the art who review this disclosure will readily appreciatethat many modifications are possible (e.g., variations in sizes,dimensions, structures, shapes and proportions of the various elements,values of parameters, mounting arrangements, use of materials, colors,orientations, etc.) without materially departing from the novelteachings and advantages of the subject matter recited. For example,elements shown as integrally formed may be constructed of multipleparts, or elements shown as multiple parts may be integrally formed, theoperation of the interfaces may be reversed or otherwise varied, thelength or width of the structures, and/or members, or connectors, orother elements of the system, may be varied, and the nature or number ofadjustment positions provided between the elements may be varied. Itshould be noted that the elements and/or assemblies of the system may beconstructed from any of a wide variety of materials that providesufficient strength or durability, in any of a wide variety of colors,textures, and combinations. Accordingly, all such modifications areintended to be included within the scope of the present innovations.Other substitutions, modifications, changes, and omissions may be madein the design, operating conditions, and arrangement of the desired andother exemplary embodiments without departing from the spirit of thepresent innovations.

Referring now to FIG. 1A and FIG. 1B, depicted is a burner 10. Accordingto various examples, the burner 10 may be utilized in outside vapordeposition (OVD) of silica soot particles 12 on a substrate 14. Thesubstrate 14 may be a bait rod, a soot preform, a core cane, othercomponents of an optical fiber preform, components of a glass article,or combinations thereof. As such, the burner 10 may be utilized in theformation of an optical fiber preform. In operation, the burner 10 isconfigured to burn or oxidize a silicon-containing fuel to produce thesilica soot particles 12 in a soot stream 16. The soot stream 16 isexpelled toward the substrate 14 such that the silica soot particles 12are deposited on the substrate 14. The ignition of thesilicon-containing fuel may occur at a lift-off distance 18 from aburner face 22 of the burner 10. (See also inset 40.)

The first gas aperture 68 receives the first gas 76 which may include afirst oxidizer and/or a first fuel stream. According to variousexamples, the first gas 76 may be premixed prior to reaching the burnerface 22 of the burner 10. In other words, the first fuel stream and thefirst oxidizer may be premixed in advance of the burner face 22 of theburner 10. For purposes of this disclosure, the term “premixed” meansthat two or more constituents (e.g., the first fuel stream and the firstoxidizer) are substantially homogeneously mixed prior to exiting burnerface 22. According to various examples, the first fuel stream and thefirst oxidizer are surface mixed at the burner face 22 of the burner 10.In such an example, the first gas 76 is substantially or fully composedof the first fuel stream, and the first oxidizer is mixed with the firstfuel stream at the burner face 22 of the burner 10. In surface mixed, ordiffusion-mixed, examples, the first oxidizer may be supplied by theambient environment (e.g., ambient oxygen) or may be provided byseparate ports, tubes or openings in the burner face 22 of the burner10. In surface mixed examples, the first fuel stream and the firstoxidizer mix downstream of the burner face 22 and prior to combustion.The first oxidizer may include O₂, an oxygen-containing gas (e.g., air),other oxygen-containing compounds, non-oxygen containing compounds(e.g., chlorine and other halide containing compounds) and/orcombinations thereof. The first fuel stream may include a firsthydrocarbon (e.g., at least one of CH₄, C₂H₆, C₃H₈, C₄H₁₀, etc.), H₂,CO, other combustible compounds and/or combinations thereof. In apreferred embodiment, the first fuel stream lacks a silicon-containingfuel. As used herein, the term “fuel” encompasses any liquid or gaswhich can be burned to produce heat, and has a flammable range with airat 20° C. and a standard pressure of 101.3 kPa. Fuels includenon-silicon-containing fuels (i.e. fuels that lack Si in thecomposition) and silicon-containing fuels (i.e. fuels that include Si inthe composition).

The fume gas opening 72 of fume tube 52 may be provided with a fume gas80 including at least one of O₂ and N₂ (i.e., an inner shield N₂ gas)and a silicon-containing fuel. The silicon-containing fuel may includeoctamethylcyclotetrasiloxane (OMCTS), decamethylcyclopentasiloxane,dodecamethylcyclohexasiloxane, hexamethylcyclotrisiloxane,hexamethyldisiloxane, octamethyltrisiloxane, decamethyltetrasiloxane,dodecamethylpentasiloxane, other silicon-containing fuels and/orcombinations thereof. The fume gas 80—exits the burner face 22 through afume tube aperture 84. In other words, the burner 10 is configured topass a silicon-containing fuel in the fume gas 80 through the fume tubeaperture 84. The fume tube aperture 84 of the fume tube 52 may have asingle diameter that extends through the fume tube 52 or the diametermay vary. The fume tube aperture 84 may have a diameter, or longestcross-sectional linear dimension at burner face 22, of about 1.0 mm, orabout 1.2 mm, or about 1.4 mm, or about 1.6 mm, or about 1.8 mm, orabout 2.0 mm, or about 2.2 mm, or about 2.4 mm, or about 2.6 mm, orabout 2.8 mm, or about 3.0 mm, or about 3.2 mm, or about 3.4 mm, orabout 3.6 mm, or about 3.8 mm, or about 4.0 mm, or about 5.0 mm, or anyand all values and ranges between these values.

A shield gas 86 may be passed through the burner 10. As used herein,“shield gas” refers to a gas that is capable of controlling heat and/ormass transfer between the silicon-containing fuel (e.g. fuel passingthrough fume tube aperture 84) and other fuel streams delivered throughburner face 22. Preferably, the shield gas is delivered at a positionbetween the silicon-containing fuel and the first gas 76. The shield gas86 may include one or more inert gases (e.g. N₂, Ar, Kr). In oneembodiment, the shield gas 86 includes a fuel other than asilicon-containing fuel; that is, the shield gas 86 includes anon-silicon-containing fuel and no silicon-containing fuel. In anotherembodiment, shield gas 86 lacks a fuel. In still another embodiment,shield gas 86 includes a non-silicon-containing fuel and an oxidizer.Examples of non-silicon-containing fuels optionally included in theshield gas 86 include hydrocarbons (e.g. CH₄, C₂H₆, C₃H₈, C₄H₁₀, etc.),H₂, CO, other combustible compounds and/or combinations thereof. Theshield gas 86 is passed through the burner 10 and ultimately exits theburner face 22 through a shield gas aperture 88. The shield gas aperture88 is preferably positioned such that the burner 10 directs the shieldgas 86 between the silicon-containing fuel (passing through fume tubeaperture 84) and the combustion of a second fuel stream and a secondoxidizer (passing as second gas 94 through secondary tubes 96) asexplained in greater detail below. The first gas 76 passes through theburner 10 and ultimately exits the burner face 22 through a plurality offirst tubes 92. The first tubes 92 are positioned proximate acircumference of the burner face 22 of the burner 10. The first tubes 92may be separate structures or may be integrally formed by the componentsof the burner 10. As such, the first gas 76 including the first oxidizerand first fuel may be passed or combusted at a periphery (outer radialregion) of the burner face 22.

A second gas 94 (i.e., sometimes referred to as a supplemental gas) mayinclude a second oxidizer and a second fuel stream. The second oxidizermay include O₂, an oxygen-containing gas (e.g., air), otheroxygen-containing compounds, non-oxygen containing compounds (e.g.,chlorine and other halide containing compounds) and/or combinationsthereof. According to various examples, the first and second oxidizersare substantially the same, but it will be understood that the first andsecond oxidizers may be different. The second fuel stream of the secondgas 94 may include at least one of a hydrocarbon (e.g. CH₄, C₂H₆, C₃H₈,C₄H₁₀, etc.), H₂, CO, other combustible compounds and/or combinationsthereof. In a preferred embodiment, the second fuel stream lacks asilicon-containing fuel. According to various examples, the first andsecond fuel streams may have substantially the same composition, but itwill be understood that the first and second fuel streams may bedifferent; that is, the first fuel stream and the second fuel streamdiffer in composition in one embodiment. The second gas 94 passesthrough the burner 10 and ultimately exits the burner face 22 through aplurality of secondary tubes 96. According to various examples, thesecondary tubes 96 are positioned between the fume tube 52 and the oneor more first tubes 92 such that the second gas 94 is passed between thefume gas 80 and the first gas 76 at the burner face 22. As such, thecombustion of the second gas 94 may occur between the combustion of thefirst gas 76 and the combustion of the fume gas 80. Similarly, inembodiments employing a shield gas, delivery of the shield gas 86 mayoccur between combustion of the first gas 76 and the combustion of thefume gas 80, or between combustion of the second gas 94 and thecombustion of the fume gas 80. It will be understood that theconstituents of the second gas 94 may be mixed upstream of the burner10, may be mixed in the burner 10 and/or diffusion-mixed at the burnerface 22. In other words, the second fuel stream and the second oxidizermay be premixed or surface mixed in a similar manner to the first fuelstream and the first oxidizer of the first gas 76.

Referring now to FIGS. 1A, 1B, and 2, in operation, the burner 10 may beused in a method 110 of producing silica soot particles 12. It will beunderstood that the method 110 may also substantially be used for theformation of an optical fiber preform or other substrate 14 which mayinclude silica soot 12. The method 110 may begin with a step 114 ofcombusting the first fuel stream and the first oxidizer of the first gas76 at the burner face 22. It will be understood that combustionoccurring “at the burner face 22” may start between about 0 mm and about2 mm from the burner face 22 and extend up to 20 mm from the burner face22 without departing from the teachings provided herein. According tovarious examples, a first equivalence ratio of the first fuel stream andthe first oxidizer of the first gas 76 is greater than about 1. In orderto accomplish step 114, the first gas 76 including the first oxidizerand the first fuel stream is passed or directed through the first tubes92 of the burner 10 to the burner face 22. Combustion of the first gas76 forms an outer or first flame 78 at the periphery (outer radialregion) of the burner 10. In examples where the combustion of the firstfuel stream and the first oxidizer is produced by surface mixing, thefirst fuel and the first oxidizer may be supplied by separate firsttubes 92 or the first oxidizer may be ambient air around the burner 10.

As explained above, the first fuel stream may include a firsthydrocarbon (e.g., at least one of CH₄, C₂H₆, C₃H₈, C₄H₁₀, etc.), H₂,CO, other combustible compounds and/or combinations thereof. The firstgas 76 may be combusted such that its combustion ignites the second gas94 (at the exit of secondary tubes 96) and the fume gas 80 including thesilicon-containing fuel. Further, the ignition of the first gas 76 mayfunction as a pilot light for the burner 10.

Flow rates and molar ratios of the first fuel and first oxidizer of thefirst gas 76 and for the second fuel and second oxidizer of the secondgas 94 depend on the compositions of the first fuel, first oxidizer,second fuel and second oxidizer. Representative flow rates based onusing methane as the first fuel and oxygen as the first oxidizer follow.One skilled in the art can determine similarly appropriate flow ratesand molar ratios for other combinations of fuels and oxidizers.

The first fuel of the first gas 76 may be passed at a flow rate of fromabout 1 slpm to about 9 slpm, or from about 1.25 slpm to about 8.75slpm, or from about 1.5 slpm to about 8.5 slpm, or from about 1.75 slpmto about 8.25 slpm, or from about 2.0 slpm to about 8.0 slpm, or fromabout 2.25 slpm to about 7.75 slpm, or from about 2.5 slpm to about 7.5slpm, or from about 2.75 slpm to about 7.25 slpm, or from about 3.0 slpmto about 7.0 slpm, or from about 3.25 slpm to about 7.75 slpm, or fromabout 3.5 slpm to about 7.5 slpm, or from about 3.75 slpm to about 7.25slpm, or from about 4.0 slpm to about 7.0 slpm, or from about 4.25 slpmto about 6.75 slpm, or from about 4.5 slpm to about 6.5 slpm, or fromabout 4.75 slpm to about 6.25 slpm, or from about 5.0 slpm to about 6.0slpm. For example, the flow rate of the first fuel in the first gas 76may be about 1.0 slpm, or about 1.25 slpm, or about 1.5 slpm, or about1.75 slpm, or about 2.0 slpm, or about 2.25 slpm, or about 2.5 slpm, orabout 2.75 slpm, or about 3.0 slpm, or about 3.25 slpm, or about 3.5slpm, or about 3.75 slpm, or about 4.0 slpm, or about 4.25 slpm, orabout 4.5 slpm, or about 4.75 slpm, or about 5.0 slpm, or about 5.25slpm, or about 5.5 slpm, or about 5.75 slpm, or about 6.0 slpm, or about6.25 slpm, or about 6.5 slpm, or about 6.75 slpm, or about 7.0 slpm, orabout 7.25 slpm, or about 7.5 slpm, or about 7.75 slpm, or about 8.0slpm, or about 8.25 slpm, or about 8.5 slpm, or about 8.75 slpm, orabout 9.0 slpm or any and all values and ranges therebetween.

The flow rate of the first oxidizer of the first gas 76 may be fromabout 1 slpm to about 9 slpm, or from about 1.25 slpm to about 8.75slpm, or from about 1.5 slpm to about 8.5 slpm, or from about 1.75 slpmto about 8.25 slpm, or from about 2.0 slpm to about 8.0 slpm, or fromabout 2.25 slpm to about 7.75 slpm, or from about 2.5 slpm to about 7.5slpm, or from about 2.75 slpm to about 7.25 slpm, or from about 3.0 slpmto about 7.0 slpm, or from about 3.25 slpm to about 7.75 slpm, or fromabout 3.5 slpm to about 7.5 slpm, or from about 3.75 slpm to about 7.25slpm, or from about 4.0 slpm to about 7.0 slpm, or from about 4.25 slpmto about 6.75 slpm, or from about 4.5 slpm to about 6.5 slpm, or fromabout 4.75 slpm to about 6.25 slpm, or from about 5.0 slpm to about 6.0slpm. For example, the flow rate of the first oxidizer in the first gas76 may be about 1.0 slpm, or about 1.25 slpm, or about 1.5 slpm, orabout 1.75 slpm, or about 2.0 slpm, or about 2.25 slpm, or about 2.5slpm, or about 2.75 slpm, or about 3.0 slpm, or about 3.25 slpm, orabout 3.5 slpm, or about 3.75 slpm, or about 4.0 slpm, or about 4.25slpm, or about 4.5 slpm, or about 4.75 slpm, or about 5.0 slpm, or about5.25 slpm, or about 5.5 slpm, or about 5.75 slpm, or about 6.0 slpm, orabout 6.25 slpm, or about 6.5 slpm, or about 6.75 slpm, or about 7.0slpm, or about 7.25 slpm, or about 7.5 slpm, or about 7.75 slpm, orabout 8.0 slpm, or about 8.25 slpm, or about 8.5 slpm, or about 8.75slpm, or about 9.0 slpm or any and all values and ranges therebetween.

According to various examples, the first gas 76 may be fuel rich or havea higher molar ratio of first fuel stream than the first oxidizer. Themol % of the first fuel stream in the first gas 76 may be from about 50mol % to about 70 mol %, or from about 50 mol % to about 68 mol %, orfrom about 50 mol % to about 66 mol %, or from about 50 mol % to about64 mol %, or from about 50 mol % to about 62 mol %, or from about 50 mol% to about 60 mol %, or from about 50 mol % to about 58 mol %, or fromabout 50 mol % to about 56 mol %, or from about 50 mol % to about 54 mol%, or from about 50 mol % to about 52 mol % or any and all values andranges therebetween. It will be understood that the molar ratio of fuelto oxidizer may also be expressed as an equivalence ratio ϕ. Theequivalence ratio is defined as the ratio of the actual fuel/oxidizerratio to the stoichiometric fuel/oxidizer ratio. Stoichiometriccombustion occurs when all the oxidizer is consumed in the reaction, andthere is no oxidizer (e.g., molecular oxygen) in the products of thecombustion. As such, an equivalence ratio of greater than 1 indicatesexcess fuel, while an equivalence ratio less than 1 indicates excessoxidizer. A first equivalence ratio of the first fuel stream to thefirst oxidizer in the first gas 76 may be about 1.0 or greater, or about1.3 or greater, or about 1.6 or greater, or about 2.0 or greater, orabout 3.0 or greater, or about 4.0 or greater, or about 5.0 or greater,or about 10 or greater, or about 50 or greater, or about 100 or greater,or about 1000 or greater, or about infinity, or in the range from about1.0 to about 100, or in the range from about 1.2 to about 50, or in therange from about 1.3 to about 25, or in the range from about 1.4 toabout 15, or in the range from about 1.5 to about 10, or in the rangefrom about 1.6 to about 8, or any and all values and rangestherebetween. Infinity occurs when no oxidizer flow is used. Forexample, the first equivalence ratio may be from about 1 to aboutinfinity, or from about 1.6 to about infinity, or from about 2 to aboutinfinity, etc.

As a result of the first fuel stream to first oxidizer equivalence ratioin the first gas 76, the first gas 76 may exhibit a first burningvelocity. For purposes of this disclosure, the term “burning velocity”is the speed at which a laminar combustion wave propagates relative toan unburned gas mixture (e.g., the first or second gases 76, 94) aheadof it. The first burning velocity of the combusted first fuel stream andfirst oxidizer of the first gas 76 may be about 5 cm/s, or about 10cm/s, or about 15 cm/s, or about 20 cm/s, or about 25 cm/s, or about 30cm/s, or about 35 cm/s, or about 40 cm/s, or about 45 cm/s, or about 50cm/s, or about 55 cm/s, or about 60 cm/s, or about 65 cm/s, or about 70cm/s, or about 75 cm/s, or about 80 cm/s, or about 80 cm/s or any andall values and ranges between these values. For example, the firstburning velocity of the second gas 94 may be from about 10 cm/s to about75 cm/s, or from about 20 cm/s to about 50 cm/s, or from about 30 cm/sto about 50 cm/s.

A step 118 of combusting the second fuel stream and the second oxidizerof the second gas 94 at the burner face 22 is performed. According tovarious examples, the second gas 94 has a second equivalence ratio ofthe second fuel stream and the second oxidizer which is less thanabout 1. Step 118 is accomplished by passing the second gas 94 includingthe second oxidizer and the second fuel stream through the secondarytubes 96 of the burner 10 and then igniting the second gas 94. Asexplained above, the second fuel stream and the second oxidizer may bepremixed in advance of the burner face 22 (i.e., prior to entering theburner 10 and/or within the burner 10). Combustion of the second gas 94forms a secondary flame 98 at an inner radial position (i.e. inside theperiphery and between outer flame 78 and fume tube aperture 84).Conventional burner designs may use additional oxygen to aid incombustion of excess fuels and silicon laden compounds. Use of thepresent disclosure, which utilizes both the second fuel stream in thesecond gas 94 and a sufficient amount of the second oxidizer to combustthe second fuel stream, imparts a variety of beneficial flamecharacteristics as explained in greater detail below. Given theplacement of the second tubes 96, the second gas 94 is passed betweenthe first gas 76 and the fume gas 80. As explained above, the secondoxygen and second fuel may be mixed to form the second gas 94 prior toentry into the burner 10, in the burner 10 or at the burner face 22.

Flow rates and molar ratios of the second fuel and second oxidizer ofthe second gas 94 depend on the compositions of the second fuel andsecond oxidizer. Representative flow rates based on using methane as thesecond fuel and oxygen as the second oxidizer follow. One skilled in theart can determine similarly appropriate flow rates and molar ratios forother combinations of fuels and oxidizers.

The second oxidizer of the second gas 94 may be passed through theburner at a flow rate of from about 12 slpm to about 36 slpm, or fromabout 13 slpm to about 35 slpm, or from about 14 slpm to about 34 slpm,or from about 15 slpm to about 33 slpm, or from about 16 slpm to about32 slpm, or from about 17 slpm to about 31 slpm, or from about 18 slpmto about 30 slpm, or from about 19 slpm to about 29 slpm, or from about20 slpm to about 28 slpm, or from about 21 slpm to about 27 slpm, orfrom about 22 slpm to about 26 slpm, or from about 23 slpm to about 25slpm. For example, the second oxidizer of the second gas 94 can bepassed at a rate of about 12 slpm, or about 13 slpm, or about 14 slpm,or about 15 slpm, or about 16 slpm, or about 17 slpm, or about 18 slpm,or about 19 slpm, or about 20 slpm, or about 21 slpm, or about 22 slpm,or about 23 slpm, or about 24 slpm, or about 25 slpm, or about 26 slpm,or about 27 slpm, or about 28 slpm, or about 29 slpm, or about 30 slpm,or about 31 slpm, or about 32 slpm, or about 33 slpm, or about 34 slpmor any and all values and ranges therebetween.

The second fuel stream of the second gas 94 may be passed at a rate offrom about 1 standard liters per minute (slpm) to about 9 slpm, or fromabout 1.25 slpm to about 8.75 slpm, or from about 1.5 slpm to about 8.5slpm, or from about 1.75 slpm to about 8.25 slpm, or from about 2.0 slpmto about 8.0 slpm, or from about 2.25 slpm to about 7.75 slpm, or fromabout 2.5 slpm to about 7.5 slpm, or from about 2.75 slpm to about 7.25slpm, or from about 3.0 slpm to about 7.0 slpm, or from about 3.25 slpmto about 7.75 slpm, or from about 3.5 slpm to about 7.5 slpm, or fromabout 3.75 slpm to about 7.25 slpm, or from about 4.0 slpm to about 7.0slpm, or from about 4.25 slpm to about 6.75 slpm, or from about 4.5 slpmto about 6.5 slpm, or from about 4.75 slpm to about 6.25 slpm, or fromabout 5.0 slpm to about 6.0 slpm. For example, the flow rate of thesecond fuel stream in the second gas 94 may be about 1.0 slpm, or about1.25 slpm, or about 1.5 slpm, or about 1.75 slpm, or about 2.0 slpm, orabout 2.25 slpm, or about 2.5 slpm, or about 2.75 slpm, or about 3.0slpm, or about 3.25 slpm, or about 3.5 slpm, or about 3.75 slpm, orabout 4.0 slpm, or about 4.25 slpm, or about 4.5 slpm, or about 4.75slpm, or about 5.0 slpm, or about 5.25 slpm, or about 5.5 slpm, or about5.75 slpm, or about 6.0 slpm, or about 6.25 slpm, or about 6.5 slpm, orabout 6.75 slpm, or about 7.0 slpm, or about 7.25 slpm, or about 7.5slpm, or about 7.75 slpm, or about 8.0 slpm, or about 8.25 slpm, orabout 8.5 slpm, or about 8.75 slpm, or about 9.0 slpm or any and allvalues and ranges therebetween.

The molar ratio of the second fuel stream and the second oxidizer in thesecond gas 94 may be such that the second gas 94 has a greater mol % ofthe second oxidizer than second fuel stream. In other words, the secondgas 94 may be said to be lean. The mol % of the second fuel stream inthe second gas 94 may be from about 1 mol % to about 49 mol %, or fromabout 1 mol % to about 40 mol %, or from about 1 mol % to about 33 mol%, or from about 1 mol % to about 30 mol %, or from about 2 mol % toabout 25 mol %, or from about 4 mol % to about 24 mol %, or from about 6mol % to about 23 mol %, or from about 8 mol % to about 21 mol %, orfrom about 10 mol % to about 20 mol %, or from about 11 mol % to about19 mol %, or from about 12 mol % to about 18 mol %, or from about 13 mol% to about 17 mol %, or from about 14 mol % to about 16 mol % or fromabout 15 mol % to about 16 mol %. For example, the mol % of the secondfuel stream in the second gas 94 may be about 1 mol %, or about 2 mol %,or about 3 mol %, or about 4 mol %, or about 5 mol %, or about 6 mol %,or about 7 mol %, or about 8 mol %, or about 9 mol %, or about 10 mol %,or about 11 mol %, or about 12 mol %, or about 13 mol %, or about 14 mol%, or about 15 mol %, or about 16 mol %, or about 17 mol %, or about 18mol %, or about 19 mol %, or about 20 mol %, or about 21 mol %, or about22 mol %, or about 23 mol %, or about 24 mol %, or about 25 mol % or anyand all values and ranges therebetween. A second equivalence ratio ofthe second fuel stream to the second oxidizer in the second gas 94 maybe about 0.1, or about 0.2, or about 0.3, or about 0.33, or about 0.4,or about 0.5, or about 0.6, or about 0.7, or about 0.8, or about 0.9, orabout 1.0 or any and all values between these values. For example, thesecond equivalence ratio would be less than 1, or from about 0.1 toabout 0.9, or from about 0.1 to about 0.8, or from about 0.1 to about0.7, or from about 0.1 to about 0.6, or from about 0.1 to about 0.5, orfrom about 0.2 to about 0.4.

As a result of the second equivalence ratio between the second fuelstream to second oxidizer in the second gas 94, the second gas 94 mayexhibit a second burning velocity. The second burning velocity of thecombusted second fuel stream and second oxidizer of the second gas 94may be about 25 cm/s, or about 50 cm/s, or about 75 cm/s, or about 100cm/s, or about 125 cm/s, or about 150 cm/s, or about 175 cm/s, or about200 cm/s, or about 225 cm/s or about 250 cm/s or any and all values andranges between these values. For example, the second burning velocity ofthe second gas 94 may be from about 50 cm/s to about 225 cm/s, or fromabout 100 cm/s to about 175 cm/s, or from about 125 cm/s to about 150cm/s.

A step 122 of combusting the silicon-containing fuel into the pluralityof silica soot particles 12 is completed. Step 122 may be accomplishedby passing or directing the fume gas 80 including at least one of O₂ andN₂ and the silicon-containing fuel through the fume tube 52 of theburner 10. As such, step 122 includes passing the silicon-containingfuel through the fume tube aperture 84. The fume gas 80 may be passed atsuch a rate that the O₂ and/or the N₂ have a flow rate through the fumetube 52 of from about 6 standard liters per minute (slpm) to about 9slpm, or from about 6.25 slpm to about 8.75 slpm, or from about 6.5 slpmto about 8.5 slpm, or from about 6.75 slpm to about 8.25 slpm, or fromabout 7.0 slpm to about 8.0 slpm, or from about 7.25 slpm to about 7.75slpm. For example, the flow rate of O₂ and/or N₂ passed through the fumetube 52 in the fume gas 80 may be about 6.25 slpm, or about 6.5 slpm, orabout 6.75 slpm, or about 7.0 slpm, or about 7.25 slpm, or about 7.5slpm, or about 7.75 slpm, or about 8.0 slpm, or about 8.25 slpm, orabout 8.5 slpm, or about 8.75 slpm, or about 9.0 slpm or any and allvalues and ranges therebetween.

As explained above, the silicon-containing fuel may includeoctamethylcyclotetra-siloxane, decamethylcyclopentasiloxane,dodecamethylcyclohexasiloxane, hexamethyl-cyclotrisiloxane,hexamethyldisiloxane, octamethyltrisiloxane, decamethyltetrasiloxane,dodecamethylpentasiloxane, other silicon-containing fuels and/orcombinations thereof. The silicon-containing fuel may be passed in thefume gas 80 at a rate of from about 12 grams per minute (gpm) to about36 gpm, or from about 13 gpm to about 35 gpm, or from about 14 gpm toabout 34 gpm, or from about 15 gpm to about 33 gpm, or from about 16 gpmto about 32 gpm, or from about 17 gpm to about 31 gpm, or from about 18gpm to about 30 gpm, or from about 19 gpm to about 29 gpm, or from about20 gpm to about 28 gpm, or from about 21 gpm to about 27 gpm, or fromabout 22 gpm to about 26 gpm, or from about 23 gpm to about 25 gpm. Forexample, the silicon-containing fuel can be passed through the fume tube52 at a rate of about 12 gpm, or about 13 gpm, or about 14 gpm, or about15 gpm, or about 16 gpm, or about 17 gpm, or about 18 gpm, or about 19gpm, or about 20 gpm, or about 21 gpm, or about 22 gpm, or about 23 gpm,or about 24 gpm, or about 25 gpm, or about 26 gpm, or about 27 gpm, orabout 28 gpm, or about 29 gpm, or about 30 gpm, or about 31 gpm, orabout 32 gpm, or about 33 gpm, or about 34 gpm or any and all values andranges therebetween.

The silicon-containing fuel is combusted under a silicon equivalenceratio to produce the plurality of silica soot particles 12. The siliconequivalence ratio may be about 1, or about 1.2, or about 1.4, or about1.6, or about 1.8, or about 2.0, or about 2.2, or about 2.4, or about2.6, or about 2.67, or about 2.8, or about 3.0, or about 3.2, or about3.4, or about 3.6, or about 3.8, or about 4.0, or about 4.2, or about4.4, or about 4.6, or about 4.8, or about 5.0 or any and all values andranges therebetween. For example, the silicon equivalence ratio may befrom about 1 to about 5, or from about 2 to about 4, or from about 2.67to about 4, or from about 2.5 to about 3.5, or from about 3 to about 4.It will be understood that the oxidizing agent which is used to combustthe silicon-containing fuel may be provided by the fume gas 80, theambient environment and/or the second oxidizer. For example, aftercombustion of the second fuel stream, excess second oxidizer (i.e., asthe second equivalence ratio is less than 1) may be utilized to combustthe silicon-containing fuel in addition to oxidizers present in the fumegas 80 to reach the silicon equivalence ratio.

Combustion of the silicon-containing fuel (i.e., the fume gas 80) intothe plurality of silica soot particles 12 occurs at the lift-offdistance 18 away from the burner face 22. As explained above, thecombustion of the silicon-containing fuel occurs by igniting thesilicon-containing fuel and/or fume gas 80 at the lift-off distance 18from the burner face 22 of the burner 10. As used herein, the lift-offdistance 18 is the shortest distance between an ignition point 132 on astable flame front of the silicon-containing fuel the burner face 22 asmeasured in a direction perpendicular to the burner face 22 (see inset40). The stable flame front may have one or more ignition points 132where the flame begins. The ignition points 132 are typically visible asthe silica soot particles 12 formed by the ignition radiate light due tothe elevated temperature of the combustion. As such, the lift-offdistance 18 is measured by imaging the burner face 22 and measuring thedistance between the closest ignition point 132 (i.e., the closestvisible light generation) and the burner face 22.

As will be explained in greater detail below, conventional silicasoot-producing assemblies may strive to lengthen the distance at whichpoint silicon-including compounds are ignited as this may lead to lowercombustion temperatures which prolong assembly life. Further,conventional systems which have attempted to shorten the ignitiondistance often result in a more dispersed and unsteady soot productionwhich lowers soot capture rate and efficiency while also creating abuildup of residue on the soot-producing assembly. Contrarily, use ofthe present disclosure allows for a relatively shorter lift-off distance18, which may allow a more concentrated and less dispersed silica sootstream 16 to be formed and aimed at the substrate 14.

The lift-off distance 18 may be about 0.05 cm, or about 0.1 cm, or about0.15 cm, or about 0.2 cm, or about 0.25 cm, or about 0.3 cm, or about0.35 cm, or about 0.4 cm, or about 0.45 cm, or about 0.5 cm, or about0.55 cm, or about 0.6 cm, or about 0.65 cm, or about 0.7 cm, or about0.75 cm, or about 0.8 cm, or about 0.85 cm, or about 0.9 cm, or about0.95 cm or any and all values and ranges therebetween. For example, thelift-off distance 18 may be from about 0.05 cm to about 0.95 cm, or fromabout 0.1 cm to about 0.95 cm, or from about 0.1 cm to about 0.9 cm, orfrom about 0.1 cm to about 0.8 cm, or from about 0.1 cm to about 0.6 cm,or from about 0.2 cm to about 0.7 cm, or from about 0.3 cm to about 0.7cm, or from about 0.3 cm to about 0.6 cm, or from about 0.4 cm to about0.6 cm.

The burner 10 may exhibit a lift-off ratio which is the lift-offdistance 18 divided by a longest cross-sectional linear dimension of thefume tube aperture 84 at burner face 22. The lift-off ratio may be about0.1, or about 0.2, or about 0.3, to about 0.33, or about 0.4, or about0.5, or about 0.6, or about 0.7, or about 0.8, or about 0.9, or about 1,or about 1.5 or about 2.0, or about 2.5, or about 3, or about 3.5, orabout 4, or about 4.5, or about 5, or about 5.5, or about 6, or about6.5, or about 7, or about 7.5, or about 8 or any and all values andranges therebetween. For example, the lift-off ratio may be from about0.1 to about 8, or from about 0.33 to about 8, or from about 1 to about8, or from about 1 to about 7, or from about 1 to about 6, or from about1 to about 5, or from about 1 to about 4, or from about 1 to about 3, orfrom about 2 to about 3, or from about 2 to about 2.5.

In operation, the second fuel stream combusts with a portion of thesecond oxidizer and heats the remaining second oxidizer from the secondgas 94. This places a very hot stream of the second oxidizer near thesilicon-containing fuel of the fume gas 80 which more vigorouslyinteracts with the silicon-containing fuel and starts the combustion tothe silica soot particles 12 closer to the burner face 22 (i.e., reducesthe lift-off distance 18) as compared to conventional designs (e.g.designs lacking the second gas configured as described herein).

As the silicon-containing fuel is ignited, it reacts with the secondoxidizer of the second gas 94 and/or the oxidizing agent of the fume gas80 to form the plurality of silica soot particles 12. The silica sootparticles 12 travel from the ignition point 132 at the lift-off distance18 in the soot stream 16 toward the substrate 14. Use of the presentdisclosure (e.g., tailoring of the lift-off distance 18 through use ofthe second gas 94) may produce a soot stream 16 having a low dispersionof the silica soot particles 12. For example, a relatively large masspercentage of the silica soot particles 12 produced by the burner 10 maypass through an “effective zone” of the soot stream 16. The effectivezone of the soot stream 16 is used for determining the dispersion of thesilica soot particles 12 and is defined at 2 cm from the surface of thesubstrate 14, has a radius of 0.6 cm (i.e., defines a circular shape)and is substantially coaxial with the fume tube 52. The mass percentageof the silica soot particles 12 passing through the effective zone maybe a measure of the efficiency of the burner 10 as a more concentratedsoot stream 16 may have a greater amount of the silica soot particles 12contact the substrate 14. The mass percentage of the silica sootparticles 12 is measured by computer modeling the setup of the burner 10and determining the mass of simulated soot particles 12 passing throughthe defined effective zone divided by the total mass of silica particles12 and multiplied by 100. A mass percentage of silica soot particles 12passing through the effective zone may be from about 30% to about 90%,or from about 40% to about 85%, or from about 50% to about 80%, or fromabout 60% to about 75%. For example, the mass percentage of silica sootparticles 12 passing through the effective zone may be about 30%, orabout 35%, or about 40%, or about 45%, or about 50%, or about 55%, orabout 60%, or about 65%, or about 70%, or about 75%, or about 80%, orabout 85%, or about 90% or any and all values and ranges therebetween. Ahigher mass percentage of the silica soot particles 12 passing throughthe effective zone generally indicates lower dispersion of the silicasoot particles 12, which may generally increase the capture efficiencyof the silica soot particles 12 on the substrate 14.

The soot stream 16 may have a relatively high mass fraction of silicasoot particles 12 as measured at the effective zone. The mass fractionof silica soot particles 12 is the weight of the silica soot particles12 within a given volume (i.e., the effective area with a giventhickness such as about 1 mm) divided by the total weight of all matterwithin the same volume once the burner 10 has reached steady stateoperation. It will be understood that balance of matter at the effectivezone may be hot gases or other combustion products. The mass fraction ofthe silica soot particles 12 as measured at the effective zone may befrom about 0.1 to about 0.6 or from about 0.2 to about 0.4. For example,the mass fraction of silica soot particles 12 may be about 0.1, or about0.12, or about 0.14, or about 0.16, or about 0.18, or about 0.2, orabout 0.22, or about 0.24, or about 0.26, or about 0.28, or about 0.3,or about 0.32, or about 0.34, or about 0.36, or about 0.38, or about0.4, or about 0.42, or about 0.44, or about 0.46, or about 0.48, orabout 0.5 or any and all values and ranges therebetween. It will beunderstood that the mass fraction of the soot stream 16 will decreasewith increasing radial distance from a centerline axis of the sootstream 16.

A step 126 of directing the shield gas 86 between the silicon-containingfuel and the combustion of the second fuel stream and the secondoxidizer may be performed. As explained above, the shield gas 86 mayinclude N₂, Kr, Ar, other inert gas, non-silicon-containing fuel and/orcombinations thereof. The shield gas 86 is passed through the burner 10such that it exits the burner face 22 through the shield gas aperture 88between the fume gas 80 and the second gas 94. The shield gas 86 may bepassed around the fume gas 80 at a rate of from about 1 slpm to about 5slpm, or from about 1.5 slpm to about 4.5 slpm. For example, the shieldgas 86 may be passed at a rate of about 1 slpm, or about 1.5 slpm, orabout 2.0 slpm, or about 2.5 slpm, or about 3.0 slpm, or about 3.5 slpm,or about 4.0 slpm, or about 4.5 slpm, or about 5.0 slpm or any and allvalues and ranges therebetween.

Formation of the silica soot particles 12 and their subsequent movementaway from the burner face 22 of the burner 10 may be utilized in asubsequent step of depositing a portion of the plurality of silica sootparticles 12 on the substrate 14. As explained above, the substrate 14may be any component used in the manufacturing of an optical fiberpreform or other silicon-containing article.

In further embodiments, gases in addition to first gas 76, fume gas 80,shield gas 86, and second gas 94 are provided to burner 10 and deliveredthrough burner face 22. Referring to FIGS. 1A and 1B, for example, oneskilled in the art would realize it is also possible to physicallymodify the burner 10 and burner face 22 such that one or more additionalgas flow streams could be flowed through additional tubes added betweenthe flow of second gas 94 through secondary tubes 96, and thesilicon-containing fuel passing through fume tube aperture 84. Theadditional gas flow stream so arranged on the modified burner 10, andexiting the modified burner face 22, could be either an additional (e.g.third or fourth) fuel (that lacks silicon), or an additional (e.g. thirdor fourth) fuel (that lacks silicon) that is pre-mixed with anadditional (e.g. third) oxidizer. It should be clear from this conceptthat the potential gas species, their flow rates, and their molar ratiosfor the additional gas flow streams would be essentially similar to thesecond gas described herein.

It will be understood that as the burner 10 is enlarged or shrunk (i.e.,due to production requirements), the volume and/or mass flow rates ofthe above-noted components used in the method 110 may correspondinglyincrease or decrease without departing from the teachings providedherein. Further, the above-noted steps may be performed in any orderand/or substantially simultaneously without departing from the teachingsprovided herein.

Use of the present disclosure may offer a variety of advantages. First,the use of the present disclosure may decrease an audible sound producedby the burner 10 while in operation. Conventional burner systems mayproduce sound having a noise level of about 100 dB or greater asmeasured at about 1 meter. Use of the present disclosure may allow theburner 10 to produce sound at a noise level of from about 60 dB to about90 dB as measured at 1 meter. Those with ordinary skill in the art willrecognize for economic reasons a plurality of burners is often used formanufacture of an optical fiber preform. Further, to enable additionalefficiencies, those with ordinary skill in the art recognize it iscommon to co-locate several optical fiber preform machines in amanufacturing area. Accordingly, the noise from combustion from aplurality of burners and a plurality of machines scales according to thelogarithmic behavior of the decibel scale. Even though the combustionprocess is contained within a soot deposition chamber, the audible noisefrom a plurality of burners and a plurality of machines can approach orexceed safety standards depending on jurisdiction and applicable law,typically requiring personal protective equipment or similar mitigationsdepending on regulations. It is therefore evident the present disclosurecan be advantaged for audible noise.

Second, the capture efficiency of the silica soot particles 12 by thesubstrate 14 may be increased relative to conventional designs. Forexample, as the mass fraction of the silica soot particles 12 which passthrough the effective zone is increased, the dispersion of the silicasoot particles 12 decreases. Such a feature is advantageous in allowinga greater amount of silica soot particles 12 to be deposited on thesubstrate 14 per pass (i.e., fewer soot particles 12 may blow past thesubstrate 14 and not get deposited). As such, a greater efficiency canbe obtained by the burner 10. Further, smaller substrates 14 may beutilized while maintaining acceptable capture efficiency rates.

Third, only minor changes to a conventional burner design may be neededto achieve higher soot capture efficiency. Conventional combustionsystems often require new parts or couplings in order to upgradecapabilities. Use of the present disclosure offers a method of providinga different set of gases to the burner 10 in order to effectuate a largechange in the operation of the burner 10. Further, as minimal or nohardware changes to the burner 10 may be required, use of the presentdisclosure may allow for little to no capital or operational costincrease.

Examples

Provided below are examples consistent with the present disclosure andcomparative examples.

Referring now to FIGS. 3A-3C, depicted is a first comparative example(i.e., Comparative Example 1). In Comparative Example 1, a combustionsystem (e.g., the burner 10) passed a mixture of gasses which wereignited. The gasses included a combined fume O₂ and fume OMCTS (e.g.,the fume gas 80 with OMCTS being the silicon-containing fuel), a shieldgas N₂ lacking a fuel (e.g., the shield gas 86), an additional gas(e.g., only the second oxidizer of the second gas 94), and a premixedstream of O₂ and CH₄ (e.g., a premixed example of the first gas 76). Theflow rate of the gasses through the combustion system are provided inTable 1 below.

TABLE 1 Fume Fume Shield Additional Premix Premix O₂ OMCTS N₂ O₂ O₂ CH₄7.25 slpm 24 gpm 3.5 slpm 16 slpm 3.2 slpm 4.25 slpm

As can be seen from FIGS. 3A-3C, the premixed O₂ and CH₄ are ignited andburn close to a surface (e.g., the burner face 22) of the combustionsystem. The flames of the burning premixed gases being close to thesurface of the combustion system produce heat and ignite the OMCTS. Asthe heat of the burning premixed O₂ and CH₄ are spaced away from theOMCTS by the additional gas, the OMCTS forms a lifted OMCTS flame at anextended ignition distance (e.g., the lift-off distance 18). Theignition of the OMCTS takes place a distance of greater than about 1 cm(lift-off distance) from a surface (e.g., the burner face 22) of thecombustion system. The ignition of the OMCTS produces a silica soot jet(e.g., the soot stream 16) extending away from the combustion system. Asboth predicted from the models of FIGS. 3A and 3B, and shown by theimage of FIG. 3C, the increased ignition distance leads to a wide anddispersed soot jet (i.e., the soot stream 16) which impacts a target(e.g., the substrate 14). The soot jet can be seen swirling (i.e.,shearing of the soot jet) around the target causing a decrease incapture efficiency of particles (e.g., the silica soot particles 12) asthe particles float away from the target.

Referring now to FIGS. 4A-4C, depicted is a first example (i.e.,Example 1) of the present disclosure. In Example 1, a substantiallysimilar combustion system to that of the Comparative Example 1 passed amixture of gasses. The gasses included a combined fume O₂ and fume OMCTS(e.g., the fume gas 80), a shield gas N₂ lacking a fuel (e.g., theshield gas 86), an additional gas (e.g., a premixed example of thesecond gas 94 including O₂ as the second oxidizer and CH₄ as the secondfuel stream), and a premixed stream of O₂ and CH₄ (e.g., the firstoxidizer and first fuel stream of first gas 76). The flow rate of thegasses through the combustion system are provided in Table 2. Theadditional gas had an equivalence ratio of less than 1 and the premixedstream of O₂ and CH₄ had an equivalence ratio of greater than 1.

TABLE 2 Fume Fume Shield Additional Additional Premix Premix O₂ OMCTS N₂O₂ CH₄ O₂ CH₄ 7.25 slpm 24 gpm 3.5 slpm 24 slpm 4.5 slpm 3.2 slpm 4.25slpm

As can be seen from FIGS. 4A-4C, the additional CH₄ in the additionalgas provides an unconventional way of reducing soot jet turbulence bydecreasing the distance between the surface and the ignition point ofthe fume OMCTS. The decrease in the turbulence of the soot jet directlyleads to a decrease in soot jet dispersion and in an increase indeposition rate and efficiency. The reduction of turbulence is due tothe ignition point of the OMCTS in Example 1 being at about 0.5 cm(lift-off distance) from the surface of the combustion system. Comparedwith Comparative Example 1, Example 1 had a flow rate for the additionalgas which was increased by 75%, of which about 16% was CH₄, and 84% wasO₂.

Referring now to FIG. 5, provided is a side-by-side comparison of thesoot jets of Comparative Example 1 and Example 1 with the effectivezones 144 superimposed. As can be seen by the comparison of the two sootjets, the soot jet of the Example 1 is less dispersed than the soot jetof Comparative Example 1. As the soot jet of Example 1 is less dispersedthan the soot jet of Comparative Example 1, the mass percentage ofsilica for Example 1 passing through the effective zone 144 is greaterthan the mass percentage of silica passing through the effective zone144 for Comparative Example 1. As such, Example 1 is more efficient thanComparative Example 1 in delivering soot to substrate 14. A higherfraction of silica soot in the flame of Comparative Example 1 isdirected around substrate 14 without depositing on substrate 14. Thefraction of silica soot that bypasses substrate 14 in ComparativeExample 1 represents a loss of silica soot that reduces the soot captureefficiency. The fraction of silica soot bypassing substrate 14 inExample 1, in contrast, is low and the soot capture efficiency is muchhigher. In addition to the mass percentage of Example 1 being greaterthan Comparative Example 1, the mass flow rate of the soot stream 16 forExample 1 is about 18% greater than for Comparative Example 1.

Referring now to FIG. 6, provided is a plot of experimentally measuredsound level as a function of frequency for two discrete conditionspreviously described herein as examples. Three curves are shown on theplot. The upper-most solid curve, having a generally negative slope, andwith typically higher measured sound levels as a function of frequency,arises from the conditions described in Table 1, and in turn modeled inFIGS. 3A-3B producing the representative image in FIG. 3C. The lowersolid curve, of similar generally negative slope, and with typicallylower measured sound levels as a function of frequency, arises from theconditions described in Table 2, and in turn modeled in FIGS. 4A-4Bproducing the representative image in FIG. 4C. The lowest curve,represented as a dashed line, is the difference between the two casesnoted above, and is plotted as the magnitude of reduction. Viainspection it is seen the magnitude of sound level reduction increasesfrom essentially 0 dB to 13 dB as frequency increases up toapproximately 5 kHz, and remains bound between essentially a 13 dB to 23dB reduction as frequency continues to increase up to 22 kHz.

Referring now to FIG. 7, provided is a plot of experimentally measuredsoot normalized deposition efficiency (Normalized Efficiency) as afunction of the equivalence ratio CH₄ in the additional gas (e.g., thesecond gas 94) (Supplemental equivalence ratio) for soot jets in ananchored state (i.e., the ignition point 132 is against the burner face22 of the burner 10), a semi-anchored state (e.g., the ignition point132 is about 0.5 cm from the burner face 22 of the burner 10) and alifted state (e.g., the ignition point is greater than 1 cm from theburner face 22 of the burner 10) for 24 slpm of O₂ in the additional gasstream. OMCTS was used as the silicon-containing fuel (26 g/min) and wassupplied with O₂ (8.5 slpm) in the fume tube (e.g. fume tube 52). Thelifted state is generated by not including a fuel in the additional gas.All the anchored and semi-anchored states contained 24 slpm of O₂ in theadditional gas stream except the lifted state which contained 16 slpm ofO₂ and is similar to the flame in comparative example 1. The depositionefficiency and normalized deposition efficiency were computed from thefollowing equations:

${{Deposition}\mspace{14mu}{efficiency}} = ( \frac{{Total}\mspace{14mu}{Mass}\mspace{14mu}{of}\mspace{14mu}{Soot}\mspace{11mu}( {SiO}_{2} )\mspace{11mu}{deposited}\mspace{14mu}{on}\mspace{14mu}{Target}}{( {( {{Total}\mspace{14mu}{OMCTS}\mspace{14mu}{flowed}} )( \frac{0.811\mspace{11mu} g\;{SiO}_{2}}{gOMCTS} )}\; )} )$${{Normalized}\mspace{14mu}{Deposition}\mspace{14mu}{efficiency}} = ( \frac{{Deposition}\mspace{14mu}{Efficiency}}{\begin{matrix}( {{Deposition}\mspace{14mu}{efficiency}\mspace{14mu}{of}\mspace{14mu} a\mspace{14mu}{flame}}  \\ {{similar}\mspace{14mu}{to}\mspace{14mu}{comparative}\mspace{14mu}{example}\mspace{14mu} 1} )\end{matrix}} )$

As can be seen in FIG. 7, the lifted state leads to a dispersed soot jetand accordingly has a low capture efficiency. The addition of theadditional CH₄ causes the flame to move to the semi-anchored state whichincreases its efficiency as the soot jet is more focused. Further, bycausing the soot stream to reach the anchored state, the soot particlesare deposited on the surface of the burner 10 and accumulate as debris,which is an undesirable side effect requiring additional processmaintenance. In the semi-anchored state, high soot capture efficiency isachieved without buildup of debris on the burner or surfaces of thecombustion apparatus. It will be obvious to those skilled in the artthat increases in capture efficiency and concomitant reductions in strayor unwanted soot particles on surfaces and components other than theoptical preform may additionally vary depending on conditions of thesoot deposition configuration. For example, the capture efficiency for agiven set of flow conditions described previously herein may beadditionally influenced by the number of burners in a plurality ofburners, the distance between such burners, the orientation of thepreform, e.g., horizontal vs. vertical, the orientation of such burnersin relation to the soot deposition target, and the direction of theflame and the resultant generated soot particles in relation to gravityand buoyant forces. Hence the deposition efficiency is appropriatelystated in normalized terms as shown in FIG. 7.

Aspect 1 of the description is:

A method of producing soot, comprising:

combusting a first fuel stream and a first oxidizer at a burner face;

combusting a second fuel stream and a second oxidizer at the burnerface, wherein the second fuel stream and the second oxidizer arepremixed in advance of the burner face and a second equivalence ratio ofthe second fuel stream and the second oxidizer is less than about 1; and

combusting a silicon-containing fuel into a plurality of soot particles,wherein the second fuel stream and the second oxidizer are combustedbetween the first fuel stream and the silicon-containing fuel.

Aspect 2 of the description is:

The method of Aspect 1, wherein the first fuel stream comprises ahydrocarbon, H₂, CO, or combination thereof.

Aspect 3 of the description is:

The method of Aspect 1, wherein the first fuel stream comprises CH₄.

Aspect 4 of the description is:

The method of any of Aspects 1-3, wherein the first fuel stream lacks asilicon-containing fuel.

Aspect 5 of the description is:

The method of any of Aspects 1-4, wherein the first fuel stream and thefirst oxidizer are premixed in advance of the burner face.

Aspect 6 of the description is:

The method of any of Aspects 1-5, wherein a first equivalence ratio ofthe first fuel stream and the first oxidizer is greater than about 1.

Aspect 7 of the description is:

The method of Aspect 6, wherein the first equivalence ratio is 1.6 orgreater.

Aspect 8 of the description is:

The method of Aspect 6, wherein the first equivalence ratio is fromabout 2 to about 3.

Aspect 9 of the description is:

The method of Aspect 6, wherein the first equivalence ratio is about2.67.

Aspect 10 of the description is:

The method of any of Aspects 1-9, wherein the second fuel streamcomprises a hydrocarbon, H₂, CO, or a combination thereof.

Aspect 11 of the description is:

The method of any of Aspects 1-10, wherein the second fuel stream lacksa silicon-containing fuel.

Aspect 12 of the description is:

The method of any of Aspects 1-11, wherein the second fuel streamdiffers in composition from the first fuel stream.

Aspect 13 of the description is:

The method of any of Aspects 1-12, wherein the second equivalence ratiois from about 0.1 to about 0.5.

Aspect 14 of the description is:

The method of any of Aspects 1-12, wherein the second equivalence ratiois from about 0.2 to about 0.4.

Aspect 15 of the description is:

The method of any of Aspects 1-12, wherein the second equivalence ratiois about 0.33.

Aspect 16 of the description is:

The method of any of Aspects 1-15, wherein a first burning velocity ofthe combusted first fuel and first oxidizer is from about 10 cm/s toabout 75 cm/s.

Aspect 17 of the description is:

The method of any of Aspects 1-15, wherein a first burning velocity ofthe combusted first fuel and first oxidizer is from about 20 cm/s toabout 50 cm/s.

Aspect 18 of the description is:

The method of any of Aspects 1-15, wherein a first burning velocity ofthe combusted first fuel and first oxidizer is from about 30 cm/s toabout 50 cm/s.

Aspect 19 of the description is:

The method of any of Aspects 1-15, wherein a second burning velocity ofthe combusted second fuel and second oxidizer is from about 50 cm/s toabout 225 cm/s.

Aspect 20 of the description is:

The method of any of Aspects 1-15, wherein a second burning velocity ofthe combusted second fuel and second oxidizer is from about 100 cm/s toabout 175 cm/s.

Aspect 21 of the description is:

The method of any of Aspects 1-15, wherein a second burning velocity ofthe combusted second fuel and second oxidizer is from about 125 cm/s toabout 150 cm/s.

Aspect 22 of the description is:

The method of any of Aspects 1-21, wherein the silicon-containing fuelis combusted into the plurality of soot particles at a lift-off distanceaway from the burner face and the silicon-containing fuel is passedthrough a fume tube aperture at the burner face.

Aspect 23 of the description is:

The method of Aspect 22, wherein a lift-off ratio of the lift-offdistance divided by a longest linear dimension of the fume tube apertureis from about 0.33 to about 8.

Aspect 24 of the description is:

The method of Aspect 23, wherein the lift-off ratio is from about 1 toabout 4.

Aspect 25 of the description is:

The method of Aspect 23, wherein the lift-off ratio is from about 2.0 toabout 2.5.

Aspect 26 of the description is:

The method of any of Aspects 1-25, wherein the first fuel stream and thefirst oxidizer are surface mixed at the burner face.

Aspect 27 of the description is:

The method of any of Aspects 1-26, further comprising:

directing a shield gas between the silicon-containing fuel and thecombustion of the second fuel stream and the second oxidizer, the shieldgas comprising an inert gas.

Aspect 28 of the description is:

The method of Aspect 27, wherein the shield gas further comprises anon-silicon-containing fuel.

Aspect 29 of the description is the method of Aspect 28, wherein theshield gas further comprises an oxidizer.

Aspect 30 of the description is:

The method of any of Aspects 1-29, further comprising:

combusting a third fuel stream at the burner face between the secondfuel stream and the silicon-containing fuel, the third fuel streamcomprising a non-silicon-containing fuel and lacking asilicon-containing fuel.

Aspect 31 of the description is:

A method of producing soot, comprising:

combusting a first fuel stream and a first oxidizer at of a burner face;

combusting a second fuel stream and a second oxidizer at the burnerface; and

combusting a silicon-containing fuel into a plurality of silica sootparticles at a lift-off distance away from the burner face, wherein thelift-off distance is from about 0.1 cm to about 0.8 cm from the burnerface and wherein the second fuel stream is combusted between the firstfuel stream and the silicon-containing fuel.

Aspect 32 of the description is:

The method of Aspect 31, wherein the lift-off distance is from about 0.1cm to about 0.7 cm from the burner face.

Aspect 33 of the description is:

The method of Aspect 31, wherein the lift-off distance is from about 0.3cm to about 0.7 cm from the burner face.

Aspect 34 of the description is:

The method of Aspect 31, wherein the lift-off distance is from about 0.4cm to about 0.6 cm from the burner face.

Aspect 35 of the description is:

The method of Aspect 31, wherein the lift-off distance is about 0.5 cmfrom the burner face.

Aspect 36 of the description is:

The method of any of Aspects 31-35, wherein the first fuel streamcomprises a hydrocarbon, H₂, CO, or combination thereof.

Aspect 37 of the description is:

The method of any of Aspects 31-35, wherein the first fuel streamcomprises CH₄.

Aspect 38 of the description is:

The method of any of Aspects 31-37, wherein the first fuel stream lacksa silicon-containing fuel.

Aspect 39 of the description is:

The method of any of Aspects 31-38, wherein the first fuel stream andthe first oxidizer are premixed in advance of the burner face.

Aspect 40 of the description is:

The method of any of Aspects 31-39, wherein the second fuel streamcomprises a hydrocarbon, H₂, CO, or a combination thereof.

Aspect 41 of the description is:

The method of any of Aspects 31-39, wherein the second fuel stream lacksa silicon-containing fuel.

Aspect 42 of the description is:

The method of any of Aspects 31-41, wherein the second fuel streamdiffers in composition from the first fuel stream.

Aspect 43 of the description is:

The method of any of Aspects 31-42, wherein the first fuel stream andthe first oxidizer are surface mixed at the burner face.

Aspect 44 of the description is:

The method of any of Aspects 31-43, further comprising:

directing a shield gas between the silicon-containing fuel and thecombustion of the second fuel stream and the second oxidizer, the shieldgas comprising an inert gas.

Aspect 45 of the description is:

The method of Aspect 44, wherein the shield gas further comprises anon-silicon-containing fuel.

Aspect 46 is:

The method of Aspect 45, wherein the shield gas further comprises anoxidizer.

Aspect 47 of the description is:

The method of any of Aspects 31-46, further comprising:

combusting a third fuel stream at the burner face between the secondfuel stream and the silicon-containing fuel, the third fuel streamcomprising a non-silicon-containing fuel and lacking asilicon-containing fuel.

Aspect 48 of the description is:

A method of producing soot, comprising:

combusting a first fuel stream and a first oxidizer at a burner face,wherein a first equivalence ratio of the first fuel stream and the firstoxidizer is from about 1.6 to about 4;

combusting a second fuel stream and a second oxidizer at the burnerface, wherein a second equivalence ratio of the second fuel stream andthe second oxidizer is from about 0.1 to about 0.5; and

combusting a silicon-containing fuel into a plurality of silica sootparticles at a lift-off distance away from the burner face, wherein thelift-off distance is from about 0.1 cm to about 0.8 cm from the burnerface.

Aspect 49 of the description is:

The method of Aspect 48, wherein the silicon-containing fuel comprisesat least one of octamethylcyclotetrasiloxane,decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane,hexamethylcyclotrisiloxane, hexamethyldisiloxane, octamethyltrisiloxane,decamethyltetrasiloxane and dodecamethylpentasiloxane.

Aspect 50 of the description is:

The method of Aspect 48 or 49, wherein at least one of the first fuelstream and the second fuel stream comprises CH₄.

Aspect 51 of the description is:

The method of any of Aspects 48-50, wherein the combustion of the secondfuel and the second oxidizer occurs between the combustion of the firstfuel and the combustion of the silicon-containing fuel from one another.

Aspect 52 of the description is:

The method of any of Aspects 48-51, wherein a first burning velocity ofthe combusted first fuel and first oxidizer is from about 10 cm/s toabout 75 cm/s and a second burning velocity of the combusted second fueland second oxidizer is from about 50 cm/s to about 225 cm/s.

Aspect 53 of the description is:

The method of any of Aspects 48-51, wherein a first burning velocity ofthe combusted first fuel and first oxidizer is from about 20 cm/s toabout 50 cm/s and a second burning velocity of the combusted second fueland second oxidizer is from about 100 cm/s to about 175 cm/s.

Aspect 54 of the description is:

The method of any of Aspects 48-51, wherein a first burning velocity ofthe combusted first fuel and first oxidizer is from about 30 cm/s toabout 50 cm/s and a second burning velocity of the combusted second fueland second oxidizer is from about 125 cm/s to about 150 cm/s.

Aspect 55 of the description is:

The method of any of Aspects 48-54, further comprising:

depositing a portion of the silica soot particles on a substrate.

Aspect 56 of the description is:

The method of any of Aspects 48-55, wherein the silicon-containing fuelis combusted under a silicon equivalence ratio of from about 2 to about4.

Aspect 57 of the description is:

The method of any of Aspects 48-55, wherein the silicon-containing fuelis combusted under a silicon equivalence ratio of from about 2.67 toabout 4.

Aspect 58 of the description is:

The method of any of Aspects 48-57, wherein the first fuel stream lacksa silicon-containing fuel.

Aspect 59 of the description is:

The method of any of Aspects 48-58, wherein the first fuel stream andthe first oxidizer are premixed in advance of the burner face.

Aspect 60 of the description is:

The method of any of Aspects 48-59, wherein the second fuel stream lacksa silicon-containing fuel.

Aspect 61 of the description is:

The method of any of Aspects 48-60, wherein the second fuel streamdiffers in composition from the first fuel stream.

Aspect 62 of the description is:

The method of any of Aspects 48-61, wherein the first fuel stream andthe first oxidizer are surface mixed at the burner face.

Aspect 63 of the description is:

The method of any of Aspects 48-62, further comprising:

directing a shield gas between the silicon-containing fuel and thecombustion of the second fuel stream and the second oxidizer, the shieldgas comprising an inert gas.

Aspect 64 of the description is:

The method of Aspect 63, wherein the shield gas further comprises anon-silicon-containing fuel.

Aspect 65 of the description is:

The method of Aspect 64, wherein the shield gas further comprises anoxidizer.

Aspect 66 of the description is:

The method of any of Aspects 48-65, further comprising:

combusting a third fuel stream at the burner face between the secondfuel stream and the silicon-containing fuel, the third fuel streamcomprising a non-silicon-containing fuel and lacking asilicon-containing fuel.

Aspect 67 of the description is:

A flame comprising the combustion product of an organosilicon compound,the flame having an ignition point situated at a lift-off distance froma face of a burner, the lift-off distance being in the range from 0.1cm-0.8 cm.

Modifications of the disclosure will occur to those skilled in the artand to those who make or use the disclosure. Therefore, it is understoodthat the embodiments shown in the drawings and described above aremerely for illustrative purposes and not intended to limit the scope ofthe disclosure, which is defined by the following claims, as interpretedaccording to the principles of patent law, including the doctrine ofequivalents.

It will be understood by one having ordinary skill in the art thatconstruction of the described disclosure, and other components, is notlimited to any specific material. Other exemplary embodiments of thedisclosure disclosed herein may be formed from a wide variety ofmaterials, unless described otherwise herein.

It will be understood that any described processes, or steps withindescribed processes, may be combined with other disclosed processes orsteps to form structures within the scope of the present disclosure. Theexemplary structures and processes disclosed herein are for illustrativepurposes and are not to be construed as limiting.

It is also to be understood that variations and modifications can bemade on the aforementioned structures and methods without departing fromthe concepts of the present disclosure, and, further, it is to beunderstood that such concepts are intended to be covered by thefollowing claims, unless these claims, by their language, expresslystate otherwise.

What is claimed is:
 1. A method of producing soot, comprising:combusting a first fuel stream and a first oxidizer at of a burner face;combusting a second fuel stream and a second oxidizer at the burnerface; and combusting a silicon-containing fuel into a plurality ofsilica soot particles at a lift-off distance away from the burner face,wherein the lift-off distance is from about 0.1 cm to about 0.8 cm fromthe burner face and wherein the second fuel stream is combusted betweenthe first fuel stream and the silicon-containing fuel.
 2. The method ofclaim 1, wherein the first fuel stream lacks a silicon-containing fuel.3. The method of claim 1, wherein the first fuel stream and the firstoxidizer are premixed in advance of the burner face.
 4. The method ofclaim 1, wherein the second fuel stream lacks a silicon-containing fuel.5. The method of claim 1, wherein the second fuel stream differs incomposition from the first fuel stream.
 6. The method of claim 1,wherein the first fuel stream and the first oxidizer are surface mixedat the burner face.
 7. The method of claim 1, further comprising:directing a shield gas between the silicon-containing fuel and thecombustion of the second fuel stream and the second oxidizer, the shieldgas comprising an inert gas.
 8. The method of claim 7, wherein theshield gas further comprises a non-silicon-containing fuel.
 9. Themethod of claim 1, further comprising: combusting a third fuel stream atthe burner face between the second fuel stream and thesilicon-containing fuel, the third fuel stream comprising anon-silicon-containing fuel and lacking a silicon-containing fuel. 10.The method of claim 1, wherein the lift-off distance is from about 0.1cm to about 0.7 cm from the burner face.
 11. The method of claim 1,wherein the lift-off distance is from about 0.3 cm to about 0.7 cm fromthe burner face.
 12. The method of claim 1, wherein the lift-offdistance is from about 0.4 cm to about 0.6 cm from the burner face. 13.A flame comprising the combustion product of an organosilicon compound,the flame having an ignition point situated at a lift-off distance froma face of a burner, the lift-off distance being in the range from 0.1cm-0.8 cm.
 14. The flame of claim 13, wherein the lift-off distance isfrom about 0.1 cm to about 0.7 cm from the burner face.
 15. The flame ofclaim 13, wherein the lift-off distance is from about 0.3 cm to about0.7 cm from the burner face.
 16. The flame of claim 13, wherein thelift-off distance is from about 0.4 cm to about 0.6 cm from the burnerface.
 17. A method of producing soot, comprising: combusting a firstfuel stream and a first oxidizer at a burner face, wherein a firstequivalence ratio of the first fuel stream and the first oxidizer isfrom about 1.6 to about 4; combusting a second fuel stream and a secondoxidizer at the burner face, wherein a second equivalence ratio of thesecond fuel stream and the second oxidizer is from about 0.1 to about0.5; and combusting a silicon-containing fuel into a plurality of silicasoot particles at a lift-off distance away from the burner face, whereinthe lift-off distance is from about 0.1 cm to about 0.8 cm from theburner face.
 18. The method of claim 17, wherein the silicon-containingfuel comprises at least one of octamethylcyclotetrasiloxane,decamethylcyclopentasiloxane, dodecamethylcyclohexasiloxane,hexamethylcyclotrisiloxane, hexamethyldisiloxane, octamethyltrisiloxane,decamethyltetrasiloxane and dodecamethylpentasiloxane.
 19. The method ofclaim 17, wherein at least one of the first fuel stream and the secondfuel stream comprises CH₄.
 20. The method of claim 17, wherein thecombustion of the second fuel and the second oxidizer occurs between thecombustion of the first fuel and the combustion of thesilicon-containing fuel from one another.